# Physics



## Lorem Ipsum (Jan 9, 2011)

Because my Physics teacher is incapable of explaining things like this, or fobs me off saying that "you study this at A-Level", I was wondering whether you guys could help me with some Physics stuff.

Firstly, what actually is a volt? I hear the term "potential difference" which makes me think it's a difference between two things, but I have no idea how one would then "change" a voltage, and generally what it is.

Secondly, apparently putting a coil of wire perpendicular to a magnetic field induces a flow of charge in that coil (from what I can remember). Why does it do this?

And finally, why does strontium emit beta radiation as opposed to alpha and gamma? What makes an element give out a particular type of radiation in decay?

Thanks for any responses!


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## Murkrow (Jan 9, 2011)

Wow, it's like you're me a couple of years ago.



Lorem Ipsum said:


> Because my Physics teacher is incapable of explaining things like this, or fobs me off saying that "you study this at A-Level", I was wondering whether you guys could help me with some Physics stuff.


My physics teacher is exactly the same, and also claimed "you study this at A-Level" and so far we've barely touched that area of electricity.

What I _think_ (emphasis on the think!) what it is is that if you have a charge, then other charged objects near it have potential energy, in the same way that masses have potential energy around other bodies of mass due to their gravity.

The volt is a way of measuring the potential at a certain point. It's the same as joules per coulomb, the formula for working out how much potential energy an object has multiplies the voltage it feels with its own charge, giving you the energy in joules.

Potential difference is when you have two points and the potential they create are different, so it's basically the potential that one point creates minus the potential from the other. (So literally the difference)

Apologies if that's incorrect, poorly explained and/or made you more confused. I'm usually okay at understanding things but appalling when it comes to explaining it to someone else.


Can't help you with your other two questions though.


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## Tarvos (Jan 9, 2011)

I'm not an electricity expert, but I can answer this for you:




> And finally, why does strontium emit beta radiation as opposed to alpha and gamma? What makes an element give out a particular type of radiation in decay?


This is a very good question. However, only elements with very high atomic mass emit alpha nuclei. Gamma radiation is dependent on the transitions of electrons in the shells. Sp whether Sr emits gamma rays is dependent on the configuration of the isotope. The amount of gamma radiation released per emission varies a lot. Check which isotope it is.

Strontium doesn't have a high enough atomic mass for alpha radiation, I believe (or maybe it does but only for a rare isotope) I believe this happens frequently. once you get to Pu and U and the like. Officially it's everything above Ni, but it doesn't happen regularly until way, way later in the periodic table.

As you can see my answer is a bit vague, but the problem is that a) there is not really a rule for these emissions. Emissions generally occur if emitting a particle would make the parent particle more energetically stable than it was previously. B) is that when you mention strontium, there are various isotopes, and they all have different decay modes :)

I'll get back to you on the voltages and magnetism later. I barely use these.


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## Zoltea (Jan 9, 2011)

Lorem Ipsum said:


> Secondly, apparently putting a coil of wire perpendicular to a magnetic field induces a flow of charge in that coil (from what I can remember). Why does it do this?


We'll have to get into light for this one. It has to do with the relation between electricity and magnetism. A ray of light traveling in one direction will have an electrical field moving up and down along a plane perpendicular to the light. At the same time there is a magnetic field moving up and down along a plane that is perpendicular to the electrical field. These two fields produce the other and end up self-propagating. So, when a coil is placed perpendicular to a magnetic field, this is basically introducing a plane perpendicular to the magnetic field in which an electrical field can be produced and it does such.


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